Tag: physics

Questions Related to physics

Which of the following statement is correct?

physics effects of electric current electric generator ac generator magnetic effects of electric current

  1. AC generator generates a higher voltage

  2. DC generator generates a higher voltage

  3. AC generator has a permanent magnet whereas a DC generator has an electromagnet

  4. There is a split-ring commutator in a DC generator but not in an AC generator

Show answer
Correct Option: D
Explanation:

The voltage generated by a generator , whether AC or DC , depends upon the rate of change of flux linked with coil .

Both type of generators usually have permanent magnets .
There is a split- ring commutator in a DC generator but an AC generator has slip - rings .
Option D is correct .

The device which converts the mechanical energy in to electric energy is

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. D.C. motor

  2. A.C. dynamo

  3. Transformer

  4. Starter

Show answer
Correct Option: B
Explanation:

The AC dynamo (generator) is made up of stationary magnets (stator) which create a powerful magnetic field, and a rotating magnet (rotor) which distorts and cuts through the magnetic lines of flux of the stator. When the rotor cuts through lines of magnetic flux it makes electricity. Thus mechanical energy is converted into electrical energy. 

Read the following statements and answer whether the given statement is true or false.


An electric generator works on the principle of electromagnetic induction.

physics effects of electric current electric generator ac generator magnetic effects of electric current

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

An electric generator works on the principle of Electromagnetic Induction.

In it, an e.m.f is induced in the coil when the magnetic flux linked with the coil changes.

Hence, the given statement is $True$.

For a dynamo which one of the following statements is correct

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. It converts electrical energy into light energy

  2. It converts kinetic energy into heat energy

  3. It converts mechanical energy into electrical energy

  4. It converts electrical energy into mechanical energy

Show answer
Correct Option: C
Explanation:

A  dynamo converts mechanical energy into electrical energy according to Faraday's Law of Electromagnetic Induction.


Answer-(C).

To convert mechanical energy into electrical energy, one can use

physics magnetism and electromagnetism electric generator ac generator magnetic effects of electric current

  1. DC dynamo

  2. AC dynamo

  3. motor

  4. (A) & (B)

Show answer
Correct Option: D
Explanation:

Dynamo is a device which converts mechanical energy into electrical energy.

Hence, both DC dynamo and AC dynamo can be used.

Hence, answer is option-(D)

The current produced in a generator armature is AC because

physics effects of electric current electric generator ac generator magnetic effects of electric current

  1. the magnetic field reverses at intervals

  2. The current in the field coils is AC

  3. the rotation of the armature causes the field through it to reverse

  4. the commutator feeds current into it in opposite directions every half cycle

Show answer
Correct Option: C
Explanation:

After every half rotation, the direction of e.m.f reverses and hence current changes its direction after a regular interval.

Hence, Answer-(C)

The value of solar constant is approximately  :

stefan's law black body radiation heat transfer thermal properties physics

  1. $ 1340\ watt/m^{2}$

  2. $ 430\ watt/m^{2}$

  3. $ 340\ watt/m^{2}$

  4. $ 1388\ watt/m^{2}$

Show answer
Correct Option: D
Explanation:

The solar constant is defined as the amount of heat energy received per second per unit area by a perfect black body placed at the surface of the Earth with its surface being held perpendicular to the direction of the sun's rays.

The value of solar constant is $1388$($\dfrac{watt}{{meter}^{2}}$) or $2$($\dfrac{cal}{{cm}{\times} {min}}$)

A heated body emits radiation which has maximum intensity at frequency $v _m$. If the temperature of the body is doubled

stefan's law black body radiation heat transfer thermal properties physics

  1. the maximum intensity radiation will be at frequency $2v _m$

  2. the maximum intensity radiation will be at frequency $\displaystyle\dfrac{1}{2}v _m$

  3. the total emitted energy will increase by a factor of $16$

  4. the total emitted energy will increase by a factor of $2$

Show answer
Correct Option: A,C
Explanation:

Wien's displacement law states maximum intensity wavength $ \lambda _{m}\propto \dfrac{1}{T}$
Also for any photon,$ \lambda \propto \dfrac{1}{\nu}$
Hence, frequency $\nu _m \propto T$
Doubling of temperature leads to doubling of frequency from $\nu _m$ to $ 2\nu _m$
From Stefan's law, power is directly proportional to $T^4$
Hence $ T \rightarrow 2T \Rightarrow E \rightarrow (\dfrac {2T}{T})^4E=16E$

The amount of radiations emitted by a black body depends on its

stefan's law black body radiation heat transfer thermal properties physics

  1. size

  2. mass

  3. temperature

  4. density

Show answer
Correct Option: C
Explanation:

The radiations emitted by the body only depend on the type of surface emitting and the temperature difference between the body and the surroundings.

The amplitudes of radiations from a cylindrical heat source is related to the distance are

stefan's law black body radiation heat transfer thermal properties physics

  1. $ A \propto 1/{d}^2$

  2. $\displaystyle A \propto \frac{1}{ d} $

  3. $ A \propto d$

  4. $ A \propto d^2$

Show answer
Correct Option: B
Explanation:

The intensity is inversely proportional to  square of distance and intensity is directly proportional to square of amplitude. So, amplitude is inversely proportional to distance.